The search for polyethylene products having an improved balance of physical properties and processability has led to the development of products having improved output capacity and ever improving end use properties such as enhanced film tear or dart impact properties.
In co-pending CA Pat. Appl. No. 2,734,167, we showed that suitably substituted phosphinimine catalysts gave narrow molecular weight distribution copolymers which when made into film showed a good balance of optical and physical properties.
Polymers and films made in the gas phase using various single site catalysts, including so called “phosphinimine” catalysts, were disclosed at Advances in Polyolefins II, Napa, Calif.—Oct. 24-27, 1999 (“Development of NOVA's Single Site Catalyst Technology for use in the Gas Phase Process”—I. Coulter; D. Jeremic; A. Kazakov; I. McKay).
In a disclosure made at the 2002 Canadian Society for Chemistry Conference (“Cyclopentadienyl Phosphinimine Titanium Catalysts—Structure, Activity and Product Relationships in Heterogeneous Olefin Polymerization.” R. P. Spence; I. McKay; C. Carter; L. Koch; D. Jeremic; J. Muir; A. Kazakov. NOVA Research and Technology Center, CIC, 2002), it was shown that phosphinimine catalysts bearing variously substituted cyclopentadienyl and indenyl ligands were active toward the gas phase polymerization of ethylene when in supported form.
There is still potential for new blend compositions exhibiting a good balance of physical properties and good processability.